The present invention relates in general to respirators and in particular to a new and useful device for supplying breathing gas into a closed, volume-driven ventilating circuit of a medical respirator, which device is capable of distinguishing consumed breathing gas from leaking breathing gas.
A device of this kind is known from U.S. Pat. No. 4,127,121. This device cannot distinguish leaks from consumed gas however.
The ventilation of the patient's lungs is effected in a closed circuit. The needed oxygen and anesthetic gas are supplied through metering devices. In these devices, the consumption is determined and the difference relative to the desired value is supplied in addition. The consumption by the patient is clinically important. However, it may be determined only in a system without leaks, or where the leaking amount is known.
The U.S. Pat. No. 4,127,121 (which is incorporated here by reference) discloses a device for a monitored supply of oxygen and anesthetic gas to a patient, operating in connection with a respirator. The respirator comprises a closed ventilating circuit with a connection to the patient, a ventilation bag, a carbon dioxide absorber, and separate metering units for supplying oxygen and anesthetic gas in controlled amounts into the ventilating circuit. Each metering unit is a final element of a control circuit including a sensor, setting means, a comparator, and a controller. The oxygen control circuit measures the oxygen concentration by means of an oxygen sensor provided in the ventilating circuit, and maintains the desired value by adjusting the oxygen supply. The anesthetic gas control circuit measures, by means of a displacement sensor provided on the ventilation bag, the movement of the top of the bag, and maintains the desired value of the anesthetic gas proportion by adjusting the supply. The gas supply values of the control circuits are indicated and evaluated as consumption by the patient.
If a leak occurs in the ventilating circuit, the indicated values are a sum of the consumption by the patient plus the leak. No breakdown of the two values is possible and no leakage warning is given.